Drobo 5N: combine Seagate ST4000DM000 with ST4000DM004


I have a Drobo 5N with 2 x 4 TB Seagate ST4000DM000 HDDs. I need to get a new one but I can’t get the same model anymore, I can only get the 4TB ST4000DM004.

Would it be compatible with the other 2? If yes, then would it make sense to buy a bigger HDD (i.e. 8TB) instead? If not, then what other HDD can I get that its fairly new but compatible.

Thank you


Hi Ed,
Your current HDDs are 5400RPM, and your initial proposal would complement them with another 5400RPM, so the answer to your first question is yes.
Whilst Drobo works with HDDs of dissimilar rotation speeds, they also state that your Drobo would be best optimised with similar speed disks.
The answer to your next question is of course yes as well, however I would look for a 5400RPM models. But here’s the kick - if you only add 1 8TB, you will not get the full benefit of the disk capacity, as Drobo then reserves additional space for expansion. To show this graphically, go to:

-select your model and add in your current disks and then some hypothetical new ones.

To get the full benefit of any additional larger disk you need to add 2 of them - but please do it sequentially, allowing the Drobo to format and integrate the first one (to green) before adding the second. The Calculator will help you understand this better.
Good luck with your expansion, and please check your firmware is up to date beforehand.

Thanks for the great answers.

I get what you say about the 2 HDDs, wasn’t aware. My firmware is up-to-date, just formatted, so this shouldn’t be a problem.

So Drobo 5N cares more about RPMs than brand or should keep the brand and model as close as possible? Just curious.

Thanks again!


Drobo actually do make some recommendations on types of HDD:

NOTE: read the fine print under each table, particularly those Drobo does not recommend.
As for mixing brands, most users do so without issue - I know that some users research their HDD brands for response, heat dissipation, noise etc. I haven’t yet mixed brands but will do so shortly, but I will still observe the same RPM across brands.